Magnetic study of pressure-induced superconductivity in the [Pd(dmit) ₂] salt with spin-gapped ground state

Static magnetic measurements have been applied for the pressure-induced superconducting state in the P2₁/m phase of EtMe ₃P[Pd(dmit)₂]₂ (Et = C₂H ₅, Me = CH₃ and dmit^2- = 1,3-dithiol-2-thione- 4,5-dithiolate, C₃S₅^2-), which exhibits valence bond (VB) ordering with a spin gap at ambient pressure. Evidence for bulk superconductivity is given. The pressure dependence of the transition temperature (T_c) is obtained in the pressure range 0.2- 0.5 GPa. A possible relation between the VB order and the superconductivity is suggested on the basis of the phase diagram. The nonlinear magnetization process is analyzed to determine the behavior of the lower critical field (H_c1).